The present invention relates to an apparatus for positioning a measuring element, for example a Doppler signal emitter or receiver, for determining the position of a blood vessel and/or the direction in which the blood flows in this blood vessel, with the measuring element being pivotably mounted, via two parallelogram-type linkage systems that are disposed at an angle to one another, in such a way as to be movable in a random fashion.
U.S. Pat. No. 4,817,621, Rune Aaslid, dated Apr, 4, 1989, which is owned by the assignee of the present application, discloses an apparatus of this general type. In this known apparatus, the free ends of the parallelogram-type linkage systems are each pivotably held on a respective reference plate, with these plates being disposed at a given angle to one another. When a patient is being examined with this known apparatus, the reference plates are placed directly against the head of the patient at predetermined locations. Although this heretofore known apparatus functions satisfactorily, the capital expenditure for such an apparatus is considerable, especially due to the large number of linkages that are required. This known apparatus is therefore not economical to manufacture. Disruptions must also be taken into consideration since the measuring element does not maintain its assumed position. A further drawback is that examinations can be conducted only when the patient is in a horizontal position, and cannot be carried out at all locations of the head. In addition, handling of the apparatus is difficult, again due to the considerable weight of the apparatus. Furthermore, a patient should not move his head when an examination is being conducted with this known apparatus, since this can lead to incorrect results, and the position of the measuring element would have to be corrected.
It is therefore an object of the present invention to provide an apparatus of the aforementioned general type for positioning a measuring element, with the novel apparatus having an extremely straightforward construction and hence being economical to manufacture and enabling a disruption-free manner of operation. However, a primary object is that the measuring element be easy to position and that it reliably remain in the assumed position, so that examinations can be carried out over a long period of time without having to undergo corrections. In addition, it should be possible to effect such examinations in nearly every position of the patient, especially in a sitting position, and it should be possible to secure the apparatus, without difficulty, on a head carrier, so that movements of the head will not adversely affect the positioning of the measuring element.